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# Coefficient of restitution Watch

1. http://www.ocr.org.uk/Images/61384-q...echanics-2.pdf -Question

On question 5i of the paper above, why can't you use the fact that the coefficent of restitution is less than or equal to 1 so you can have {3u(1 – k)/k + u/2 } divided by 4u is less than or equal to 1
2. (Original post by runny4)
http://www.ocr.org.uk/Images/61384-q...echanics-2.pdf -Question

On question 5i of the paper above, why can't you use the fact that the coefficent of restitution is less than or equal to 1 so you can have {3u(1 – k)/k + u/2 } divided by 4u is less than or equal to 1
I'm actually not too impressed by the setting of this question. It clearly asks for a range of values for . The mark scheme seems to not only state that is OK as a lower bound, but also that it's not important (as indicated by the brackets).

As it turns out, the given lower bound is sometimes incompatible with Newton's Law of restitution (which requires for a 'realistic' inelastic collision) - Unless they're OK with the particles exploding upon impact i.e. OK with , which isn't usually permissible at A-Level.

An upper limit can be obtained similarly by considering (again, assuming a realistic collision) but it is less strong than the one you obtain from the velocity.
3. (Original post by Farhan.Hanif93)
...
PRSOM.
4. (Original post by Farhan.Hanif93)
I'm actually not too impressed by the setting of this question. It clearly asks for a range of values for . The mark scheme seems to not only state that is OK as a lower bound, but also that it's not important (as indicated by the brackets).

As it turns out, the given lower bound is sometimes incompatible with Newton's Law of restitution (which requires for a 'realistic' inelastic collision) - Unless they're OK with the particles exploding upon impact i.e. OK with , which isn't usually permissible at A-Level.

An upper limit can be obtained similarly by considering (again, assuming a realistic collision) but it is less strong than the one you obtain from the velocity.
thank you for this brilliant reply but i would like to ask what you mean by your last sentence which ends with 'it is less strong than the one you obtain from the velocity'. Surely narrowing down the limits more is better
5. (Original post by runny4)
thank you for this brilliant reply but i would like to ask what you mean by your last sentence which ends with 'it is less strong than the one you obtain from the velocity'. Surely narrowing down the limits more is better
If you work it through, the condition leads to , whereas the positivity of the velocity requires . But so the velocity condition 'narrows the range' the most i.e. it is stronger than the restitution condition.
6. (Original post by Farhan.Hanif93)
If you work it through, the condition leads to , whereas the positivity of the velocity requires . But so the velocity condition 'narrows the range' the most i.e. it is stronger than the restitution condition.
ok thank you very much

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